My house has a big freestanding chimney in the middle of the house. Where it goes through the ceiling, it is 3’x6′. The attic is unheated. It seems to me that this is a huge thermal bridge from the interior to the exterior. I’m considering wrapping the chimney with insulation in the attic. Anybody have any wisdom to shed?
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This is a masonry chimney?
With a masonry chimney it would in theory make sense to insulate the first six feet or so beyond the heated space, to in effect give you the insulating character of several feet of masonry vs the foot or so you have now. Whether this would make $$ sense in practice is hard to say.
You may want to be a little careful about what you choose for insulation. Should the flue liner fail and allow flames/heat to get out horizontally, it's probably not a good idea to have flammable foam right against it, eg. This isn't a real big risk, just something to think about.
Be aware that the chimney probably contains hollow areas around the flues. Air convection in these areas may be a more significant heat loss than the conduction of the masonry.
Good question.
Personally, I'd think it a bad idea. No reason other than I feel that way..hows that for useless help?
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I know it'd help the draw.
My center chimney is 3 by 10 feet and I am considering insulations, also. I think 2" of the blue foam would work okay. I am thinking of leave it exposted near the roof rafters so that I can see any water leaks through the stone or flashing. I think you could see potential fire risks before they become dangerous if you inspected the chimney every year.
I really don't think you are going to get much for your effort. You have as much heat conduction to the inside flue as to the outside (if its cold). Also, if you do decide to put anything against the brick, make sure its totally fire-proof.
For my fireplace, I did exactly the opposite - I put a standoff gap around it with plywood to make sure nothing touches it. I don't want any hot-spots conducting to any material in the attic. There are lots of other options to improve the envelope.